She uses just the one name, but don’t be fooled by that brevity. Dessa, a rapper from Minneapolis, has earned a following with her song-writing skills and her work with the hip hop collective Doomtree. Also in this show: In 1973, the American war against communism in Laos ended, leaving their Hmong allies behind; and in a room across from Carnegie Hall, the exuberant young piano phenom Lang Lang demonstrates how he approaches a Brahms Intermezzo.